The invention relates to beam-forming antenna arrays generally and, more specifically, to slotted-waveguide type arrays as commonly employed in radar systems.
Slotted-waveguide antenna arrays are well known in the art. The slot patterns used, most often in the narrow wall of a rectangular waveguide, vary according to the design objectives. The angle of incline of the slots at their spacing are dictated according to well known criteria based on bandwidths, grating lobe considerations, and polarization objectives.
U.S. Pat. No. 3,740,751 shows a slotted waveguide array in which the slots are in pairs for the accomplishment of a specific purpose therein described.
Slot arrays have been recognized as an attractive element for antenna systems since they allow the efficient distribution and radiation of electromagnetic fields with precise control of the aperture illumination and, therefore, the far-field patterns. The prior art slotted waveguide array system, however, is limited to the formation of one beam in space at a single excitation frequency in the plane parallel to the array length. This can be a major limitation for radar applications where monopulse or simulraneous multiple beams are required in the plane of the slot array.
Recognizing the existence of slotted waveguide arrays in the prior art and the limitations thereof, the manner in which the present invention permits the formation of a pair of beams will be evident as this description proceeds.